This invention relates to a method and apparatus for attaching a probe in a non-invasive manner to the skin of a patient. The invention also involves the control of pressure/vacuum internally or externally of the tube, for example, the controlled reduction of vacuum in the tube. In one specific arrangement, the invention relates to a non-invasive medical probe in which a suction cup is secured to a patient""s skin, for example the scalp of a foetus, and a method of using the probe.
In EP-A-0525021 there is described a non-invasive medical probe for monitoring a patient""s condition. The probe comprises a source of suction, which may be a bellows, or other type of pump, connected by a tube to a resilient walled suction cup for application to a patient""s skin. With the suction cup in contact with the patient""s skin, the bellows or other pump is actuated to apply vacuum through the tube to secure the cup to the patient""s skin. Mounted within the cup is an electrode for making contact with the patient""s skin following evacuation of the cup, the resilience and form of the cup being such that the resilient wall deforms so that the electrode is drawn down relative to the peripheral rim of the cup and makes the required contact with the patient""s skin. A signal is thereby obtained at the skin surface which is responsive to a varying condition of the patient. In the particular embodiment described, the suction cup is for attachment to the scalp of a foetus with the rim of the cup in sealing contact with the surface of the scalp.
A relatively high vacuum is required to secure the suction cup. The probe needs to remain attached for long durations, e.g. hours, but this creates a red mark on the skin the size of the suction cup. While not harmful, the mark is unsightly and may take up to a day to fade away. It is thus undesirable.
However, it has been found that the level of vacuum which is necessary to maintain the cup in place even during movements of the foetus head can be substantially lower than the initial vacuum necessary to secure the cup.
According to the invention there is provided a method of controllably reducing vacuum in a non-invasive medical probe having a source of vacuum interconnected with a suction cup by a resilient walled tube, comprising creating a valve aperture in the wall of the tube at a desired location through which aperture no appreciable leakage will occur when vacuum is applied and the tube is in a relaxed state, whereby with the suction cup secured by vacuum on a patient""s skin, application of a force to the tube wall will open the aperture and permit a controlled reduction of vacuum in the suction cup to a specified amount, and releasing the force will permit the aperture to close so that lower vacuum is maintained and the suction cup continues to be secured on the patient""s skin.
The step of maintaining lower vacuum mentioned throughout includes either constant or varying vacuum consistent with the suction cup or other applicator remaining secured.
In the preferred embodiment of the invention the probe is adapted for application to the scalp of a foetus with the rim of the suction cup in sealing contact with the surface of the scalp.
The invention also provides a method of enabling a controlled flow into a resilient walled tube inside which the pressure is lower than outside the tube, comprising creating a valve aperture in the wall of the tube in a desired location through which no appreciable leakage will occur when the tube is in a relaxed state, but which aperture will open on application of a force to the tube wall and permit a controlled flow therethrough into the tube, and which aperture will close when the force is released.
The invention further provides a method of controlling flow into a resilient walled tube inside which the pressure is lower than outside the tube, which tube has in its wall a preformed valve aperture capable of opening and closing when a force on the tube is respectively applied and released, the method comprising applying said force to open the aperture and to permit a controlled flow therethrough into the tube, and releasing said force so that the aperture closes and the flow stops.
The term controlled flow means flow which can be accurately interrupted at predetermined levels of pressure inside or outside the tube and/or the magnitude of the flow can be accurately adjusted. Such interruption is effected by releasing said force to allow the aperture to close, and adjusting the flow is effected by varying the applied force.
In one embodiment, the tube contains a vacuum, and upon opening the valve aperture the vacuum in the tube is controllably reduced so that lower vacuum is maintained in the tube. Preferably the tube interconnects a source of vacuum and a suction applicator.
Alternatively, upon opening the valve aperture, an overpressure outside the tube is controllably reduced or a controlled flow into the tube is generated. Preferably the portion of the tube containing the valve aperture is located or adapted for location in a chamber containing a fluid at said higher pressure. In this case, the force to open the valve aperture may be remote controlled from outside the chamber.
Preferably the vacuum reduction/pressure flow occurs at a substantially constant rate and/or amount.
It is also preferred that said force on the tube wall is applied by bending. Preferably the bending force acts through the valve aperture thereby opening the valve aperture.
The valve aperture may be created by piercing the tube wall radially, e.g. by a needle having an end which is chamfered to a V-shape to form a line end. Preferably the line end of the needle is orientated transversely to the axis of the tube.
Slicing transversely through a resilient tube to a depth which reaches the inside is known for creating a valve which opens when the tube is bent and shuts when the tube returns to a relaxed state, but the ingress of air during bending of the tube cannot be controllably stopped at a specific level or the rate of flow adjusted, especially when a relatively small quantity of fluid is involved.
The invention still further provides a non-invasive medical probe comprising a source of vacuum interconnected with a suction cup by a resilient walled tube, the cup being adapted to be secured by vacuum on a patient""s skin, wherein means are provided for controllably reducing the vacuum to a specified amount, after which lower vacuum can be maintained until the cup is removed.
Preferably the control means are provided in a tube and preferably is a valve aperture in the wall of the tube at a desired location through which aperture no appreciable leakage will occur when vacuum is applied and the tube is in a relaxed state, whilst with the suction cup secured on the patient""s skin application of a force to the tube wall will open the aperture and permit a controlled reduction of vacuum in the suction cup to the specified amount, and releasing the force will permit the aperture to close so that lower vacuum is maintained and the suction cup continues to be secured on the patient""s skin.
The source of suction is preferably a bellows attached to one end of the tube.
For bending the tube in a specific manner and location to open the valve aperture, the tube is preferably provided with finger holding means, preferably adapted to be used single-handedly.
Means may be provided for measuring the reduction in vacuum. The measuring means may be a calibrated elongate member, which in the case of the source of suction being a bellows or other expandable means for creating suction extends longitudinally of the suction means.
The invention still further provides a non-invasive medical probe comprising a suction cup adapted to be secured by vacuum to a patient""s skin and supporting an electrode, a source of vacuum, and a resilient walled tube structure connecting the source of vacuum to the suction cup, wherein the source of vacuum comprises a resilient bellows operative when fully compressed then released to apply to a predetermined low level of vacuum to the suction cup and means for enabling the bellows to be further extended manually in order to increase the vacuum applied to the suction cup to a higher level.